The Smithsonian Institution Castle located on the National Mall in Washington, D.C., was built between 1847 to 1851 when British scientist James Smithson left his estate to the United States to found "at Washington, under the name of the Smithsonian Institution, an establishment for the increase and diffusion of knowledge."
Since then, the Smithsonian has grown to over 19 museums spread throughout Washington, D.C., and are considered some of the best museums in the world. The museums include thousands of rare or significant artifacts housed in the Natural History Museum, both Air & Space Museums, American History Museum and several art museums. Virtually all the museums are FREE to the public, 364 days a year, but closed on Christmas.
Statue of Joseph Henry, first Secretary of the Smithsonian.
I live within driving distance for a day trip to these museums and visit with my family as often as I can, and if I had to pick a favorite one, it would be the National Museum of Natural History, which is directly across the National Mall from the Smithsonian Castle. But who can pick just one? They are all some of the best museums on the planet and any trip to the Washington area should include a day dedicated to seeing a few of them.